1. Field of the Invention
The present invention relates to a biochemical reaction treatment device, and more particular to a nucleic acid specimen treatment device for testing existence of genes derived from disease germs in a sample such as blood.
2. Description of the Related Art
Many methods are proposed which adopt a hybridization reaction using a probe carrier represented by a DNA microarray as a method for quickly and precisely analyzing a base sequence of nucleic acids and detecting target nucleic acids in a nucleic acid specimen. To obtain the DNA microarray, a probe having a base sequence complementary to the target nucleic acids is fixed on a solid phase such as a bead and a glass plate with high density, and a method for detecting the target nucleic acids using the DNA microarray generally has following steps.
In a first step, the target nucleic acids are amplified by an amplification method represented by a PCR method. Concretely, first and second primers are first added to the nucleic acid specimen, and a temperature cycle is applied (hereinafter referred to as “1st PCR”). The first primer is specifically bounded with some of the target nucleic acids, and the second primer is specifically bounded with some of the nucleic acids complementary to the target nucleic acids. When double-stranded nucleic acids including the target nucleic acids are bounded with the first and second primers, the double-stranded nucleic acids including the target nucleic acids are amplified by an elongation reaction.
After the double-stranded nucleic acids including the target nucleic acids are amplified sufficiently, substances other than amplified double-stranded nucleic acids such as non-reacted primers and fragments of nucleic acids are removed by purification. Methods for adsorbing the double-stranded nucleic acids to magnetic particles or methods using a column filter are known as a purification method.
After completion of purification, a third primer is added to the nucleic acid specimen, and the temperature cycle is applied (hereinafter referred to as “2nd PCR”). The third primer is marked with an enzyme, a fluorescent material, a luminescent material or the like, and is specifically bounded with some of the nucleic acids complementary to the target nucleic acids. When the third primer is bounded with the nucleic acids complementary to the target nucleic acids, the target nucleic acids marked with the enzyme, the fluorescent material, the light-emitting material or the like are amplified by the elongation reaction. As a result, when the nucleic acid specimen includes the target nucleic acids, the marked target nucleic acids are generated, and when the nucleic acid specimen does not include the target nucleic acids, the marked target nucleic acids are not generated.
In a second step, the nucleic acid specimen is brought into contact with the DNA microarray, and is hybridized with the probe of the DNA microarray. Concretely, the temperatures of the DNA microarray and the nucleic acid specimen are increased. If there is any target nucleic acid complementary to the probe, the probe and the target nucleic acids form a hybrid material.
In a third step, the target nucleic acids are detected. For example, when the maker materials are fluorescent materials, the fluorescent materials are excited by a laser and the like to measure a luminance thereof. That is to say, whether the probe and the target nucleic acids form the hybrid material or not can be detected by marker materials of the target nucleic acids, thereby confirming a specific base sequence.
Such a DNA microarray utilizing this hybridization reaction is expected for application to a medical diagnosis for specifying the disease germs and a gene diagnosis for testing constitutions of patients. A diagnosis method using such a DNA microarray utilizes a few kinds of liquids while exchanging disposable pipette tips at a pipette tip. Therefore, this operation is very complicated, and a treatment capability is limited in a manual operation. To solve these problems, some devices are proposed which automate an amplification step, a hybridization step, a detection step and a dispensing step for moving and mixing the liquid.
Now, one example of a DNA testing device is shown in FIG. 5. In FIG. 5, a constitution using one pipette is shown. A DNA testing device 101 comprises a dispensing unit 102, a base 108, a pipette tip case 110, an amplification plate 120 and a hybridization plate 130. The dispensing unit 102 can freely move in a space in the device by Z-direction moving means 104, X-direction moving means 105, and Y-direction moving means 106 and 107. Here, the Z-direction is defined as a direction perpendicular to an XY-plane in FIG. 5. Also, the dispensing unit 102 has a nozzle holding part 103, and the nozzle holding part 103 is fitted with a pipette tip 111. The pipette tip is mounted by moving the nozzle holding part 103 to the pipette tip 111 of the pipette tip case 110. The dispensing unit 102 to which the pipette tip 111 is mounted can move the liquid contained in a well 121 of an amplification plate 120 or a well 131 of a hybridization plate 130 by a pipette mechanism (not shown) to another well. The liquid is moved and mixed, and temperature control means (not shown) controls the temperature of the liquid, so that a biochemical reaction can be promoted.
The constitution using only one pipette as shown in FIG. 5 requires considerable times to treat a plurality of samples even in the case of an automated device. Therefore, as described in Japanese Patent Application Laid-Open Nos. H09-96643 and 2003-274925, devices for simultaneously treating a plurality of samples with a plurality of pipettes have been proposed.
In the constitutions described in Japanese Patent Application Laid-Open Nos. H09-96643 and 2003-274925, an action that the pipette treating a certain sample passes on the well holding a reagent for another sample may be inevitable. During movement of the reagent, the liquid held in the pipette tip might drop as micro-droplets due to vibrations and the like of a carrying shaft. When the liquid including the other sample is mixed with the reagent, it becomes a cause of misjudgment at the time of diagnosis.